Arterial stenosis is one of the most serious forms of arterial disease. In clinical practice, stenosis severity is estimated by using either simple geometrical parameters, such as determining the percent diameter of a stenosis, or by measuring hemodynamically based parameters, such as the pressure-based myocardial Fractional Flow Reserve (FFR). FFR is an invasive measurement of the functional significance of coronary stenoses. The FFR measurement technique involves insertion of a 0.014″ guidewire equipped with a miniature pressure transducer located across the arterial stenosis. It represents the ratio between the maximal blood flow in the area of stenosis and the maximal blood flow in the same territory without stenosis. Earlier studies showed that FFR<0.75 is an accurate predictor of ischemia and deferral of percutaneous coronary intervention for lesions with FFR≥0.75 appeared to be safe.
An FFR cut-off value of 0.8 is typically used in clinical practice to guide revascularization, supported by long-term outcome data. Typically, an FFR value in a range of 0.75-0.8 is considered a ‘grey zone’ having uncertain clinical significance.
Modeling vascular flow and assessing vascular flow is described, for example, in U.S. published patent application number 2012/0059246 of Taylor, to a “Method And System For Patient-Specific Modeling Of Blood Flow”, which describes embodiments which include a system for determining cardiovascular information for a patient. The system may include at least one computer system configured to receive patient-specific data regarding a geometry of at least a portion of an anatomical structure of the patient. The portion of the anatomical structure may include at least a portion of the patient's aorta and at least a portion of a plurality of coronary arteries emanating from the portion of the aorta. The at least one computer system may also be configured to create a three-dimensional model representing the portion of the anatomical structure based on the patient-specific data, create a physics-based model relating to a blood flow characteristic within the portion of the anatomical structure, and determine a fractional flow reserve within the portion of the anatomical structure based on the three-dimensional model and the physics-based model.
Additional background art includes:    U.S. Published Patent Application No. 2012/053918 of Taylor;    U.S. Published Patent Application No. 2012/0072190 of Sharma et al;    U.S. Published Patent Application No. 2012/0053921 of Taylor;    U.S. Published Patent Application No. 2010/0220917 of Steinberg et al;    U.S. Published Patent Application No. 2010/0160764 of Steinberg et al;    U.S. Published Patent Application No. 2012/0072190 of Sharma et al;    U.S. Pat. No. 6,236,878 to Taylor et al;    U.S. Pat. No. 8,311,750 to Taylor;    an article titled: “Determination of fractional flow reserve (FFR) based on scaling laws: a simulation study” by Jerry T. Wong and Sabee Molloi, published in Phys. Med. 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The disclosures of all references mentioned above and throughout the present specification, as well as the disclosures of all references mentioned in those references, are hereby incorporated herein by reference.